For example, Patent Document 1 and Patent Document 2 disclose a flowmeter provided with a sensor passage connected to an inflow passage and an outflow passage and a bypass passage placed with respect to the sensor passage. A to-be-measured fluid flows in the inflow passage, and then the fluid is divided into the one flowing in the sensor passage and the other one flowing in the bypass passage. The to-be-measured fluid having flown in the inflow passage partly flows in the sensor passage at a flow rate at which a sensor-side resistance (a differential pressure between an upstream-side pressure and a downstream-side pressure) generated in the sensor passage and a bypass-side resistance (a differential pressure between an upstream-side pressure and a downstream-side pressure) generated in the bypass passage are balanced. The to-be-measured fluid having flown out of the sensor passage and the fluid having flown out of the bypass passage are merged in the outflow passage and flown out of the flowmeter. The flowmeter measures the flow rate of the to-be-measured fluid flowing through the sensor passage by use of the sensor disposed therein, converts the measured flow rate into an entire flow rate of the to-be-measured fluid flowing through the flowmeter by a ratio (a distribution ratio) of the sensor-side resistance to the bypass-side resistance, and then outputs a signal.